Computer-aided Tomography (CT) (such as X-ray, Positron Emission Tomography (PET), etc.) and Magnetic Resonance (MR) based imaging systems commonly control and sense the location (and/or orientation) of the patient and/or the image sensing/producing equipment to produce a recorded image of a patient's anatomy that is assembled from multiple image data collections from different portions of the patient's anatomy. The patient is typically instructed to hold their breath and remain motionless during the imaging procedure in order to keep anatomy positions as constant as possible in each image data collection and thus, create as continuous and anatomically correct a recorded image as possible out of the assembled multiple image data collections.
When such systems are used in a real time mode, the time required for image data collection and/or image data processing and/or the designed field of view of the image sensing/producing equipment limits the portion of the anatomy that can be displayed in the rapidly updated manner that is referred to as “real time”.
Attempting to widen the field of view typically introduces noticeable and annoying time delays between the displayed image and the actual condition of the anatomy and/or requires impractically rapid patient and/or equipment position changes. When attempting to guide a medical device in the anatomy and record locations in the anatomy, real time imaging is desired and these problems become particularly bothersome.
The real time image's limited field of view makes the anatomical context of the real time image or a diagnosis based on tissue image properties and/or their relationship to the adjacent anatomy difficult to interpret. Thus, the location of the medical device relative to the adjacent anatomy or anatomy landmarks as shown in the real time image can be difficult to determine or time consuming to determine.
Additionally, a tissue diagnosis based on the real time image can be difficult to determine or time consuming to determine. Often one must take the additional time to create and examine a recorded wider field of view image to determine a tissue diagnosis or device location relative to the anatomy. Medical operations employing medical devices, especially percutaneous catheter-based procedures, are often best or necessary to perform when the patient is conscious; and these procedures are much longer than the time required to make a recorded image with a wide field of view of the anatomy. It is not very practical to expect the patient to hold their breath in a repeatable manner on command or to be able to remain perfectly still on the positioning table during the medical operation and real time imaging.
While locations recorded in the real time image reference frame will be correct relative to the anatomy in that particular very transitory real time image, the anatomy will move between real time images due to the patient's breathing and/or inability to remain motionless for long periods of time. Therefore, the distances between locations recorded in real time image reference frame and between recorded locations and anatomical structures in real time image reference frame will be uncertain or in error by the amount (and timing) of this uncontrolled patient motion.
This uncertainty or error is undesirable in many situations, such as when attempting to control the spacing of a therapy applied by a medical device using imaging. These problems are greatly accentuated in conventional ultrasonic based imaging systems, because the field of view of ultrasonic systems is typically much smaller than CT and MR based imaging systems. Additionally, the image sensing/producing equipment (the imaging probe) of conventional ultrasonic systems is manually positioned and its location and/or orientation is not controlled or sensed by the imaging system.
There have been various developments in the medical imaging techniques and their applications. Maintz, et al. presented “A Survey of Medical Image Registration” in Medical Image Analysis, Vol. 2, No. 1, pp 1-36, 1998. Terry M. Peters presented “Review—Image-guided surgery: From X-rays to Virtual Reality” in Computer Methods in Biomechanics and Biomedical Engineering, Vol. 4, No. 1, pp. 27-57, 2000.
Friemel, et al. (U.S. Pat. No. 5,655,535) presented a method to obtain compounded field of view ultrasound image from correlated frames of ultrasound image data. Frames of sensed echo signals are processed to detect probe motion without the use of a dedicated position sensor or motion sensor. Correlating the frames is used to detect the motion of the ultrasound probe. Image registration is performed for correlated portions to compound a large ultrasound image.
Burt, et al. (U.S. Pat. No. 5,999,662) presented a method to automatically generating a mosaic from a plurality of input images. In one example of Burt, et al., a scene of interest is illustratively captured in four video frames. Additionally, a person is walking through the scene from left to right. The images of the scene are aligned and combined using batch sequencing to produce a mosaic containing background. The residuals represent object motion relative to the background, e.g., the person walking through the scene. The image alignment process automatically aligns one input image to another input image.
Hibbard, et al. (U.S. Pat. No. 6,266,453) presented a method for automated image fusion /alignment of 3-D images. In the method of Hibbard, et al., a GUI is used to simultaneously display two 3-D image data volumes. One of the 3-D image data volumes is held constant while the other may be scaled, rotated, and translated to align homologous anatomic features. Hibbard, et al. also suggest that the image can be aligned automatically through computation based on mutual information (“MI”) maximization and the automated alignment, using MI maximization, may be performed before, after or instead of, manual alignment.
Jago (U.S. Pat. No. 6,416,477) also presented another method to produce spatially compounded panoramic ultrasound images.
Heilbrun, et al. (U.S. Patent Application Publication No. 2001/0039421) presented a method for photogrammetric surgical localization, in which the 3-D framework of the workspace can be aligned with the 3-D framework of any selected volume scan, such as MRI, CT, or PET, so that the instrument can be localized and guided to a chosen feature. To provide object recognition and location of medical instruments and the like in the image field, a digitized image pair made prior to the introduction of the instrument into the workspace is compared to an image pair made with the instrument in substantially complete view, and background subtraction-is used to remove static objects in the image field. After the image has been appropriately filtered to sharpen the image and enhance object edges, edge detection is performed for geometric recognition. Once the instrument is identified, its orientation and tip location are determined in terms of coordinates in the 3-D workspace.
Burdette, et al. (U.S. Patent Application Publication No. 2003/0135115) presented a method to determine the location of a biopsy needle within a target volume. In the method of Burdette, et al., images of the target volume is generated and spatially registered. A three-dimensional representation of the target volume is then generated from the spatially registered images. After the location of the biopsy needle in the three-dimensional target volume representation is determined, the determined biopsy needle location is correlated with the spatially registered images. For example, when the target volume representation is displayed graphically, the target volume representation also includes a graphical depiction of the determined biopsy needle location. The needle may stand out in bright contrast to the surrounding tissues in an ultrasound images, and as such, known pattern recognition techniques such as edge detection methods can be used to identify the needle's location in the ultrasound images. Because the images are spatially registered, the location of the biopsy needle relative to the coordinate system is determinable.
Burdette, et al. (U.S. Pat. No. 6,129,670) presented a system for developing a therapy plan for treatment of an organ of the patient. A translucent volume image of a portion of a patient's body, a separate translucent image of the patient organ and a translucent article image are superimposed to enable viewing of the article image simultaneously with the patient organ and a portion of the patient's body.
Gronningsaeter, et al. (U.S. Pat. No. 6,019,724) presented a method for ultrasound guidance during surgical, therapeutic or diagnostic procedures. One can correlate an in on-site ultrasound 3-D image with a 3-D data set from a previously acquired image data base and make these coordinate sets coincide with each other as well as coincide with the tool location coordinate system. In an example for open brain tumor surgery, Gronningsaeter, et al. suggest that the location of the tool can be detected in the overview image by temporal high pass filtering if the tool is continuously moving. One way to perform temporal high pass filtering is to subtract two 2-D or 3-D data sets to cancel stationary targets and highlight the moving tool. In another example, Gronningsaeter, et al. describe that after a physician marks the desired point for the radiation field center in the ultrasound image, the coordinates of this point are transferred to the coordinate system of the simulator and the direct feedback of target location will aid the placement of radiation fields and their relative angles to the patient.
Urbano, et al. (U.S. Pat. No. 6,004,270) presented an ultrasound system for contrast agent imaging and quantification in echocardiography using template image for image alignment. According to Urbano, et al., a stored template image and a real-time image are simultaneously displayed on an image display. The simultaneously displayed images have a visually perceptible effect when the real-time image becomes closely aligned with the template image at the same selected time period during the physiologic cycle. After alignment is achieved, a difference image is calculated, stored and displayed. The template image improves the alignment process of pre-contrast and post-contrast images, or pre-event/post-event difference images.
Yanof, et al. (U.S. Pat. No. 6,149,592) presented a method to electronically correlate a fluoroscopic image coordinate system and a volumetric image coordinate system and to display the volumetric image data (CT) together with at least a portion of the fluoroscopic images superimposed on the volumetric image data to show an image of said surgical instrument relative to said volumetric image data.
Hossack, et al. (U.S. Pat. No. 6,352,511) presented a medical diagnostic ultrasound system and method for post processing. According to Hossack, et al., for further enhancement of re-persistence, the recovered frames of ultrasound data are aligned or substantially aligned prior to re-persisting. The frames of ultrasound data are aligned as a function of a region of interest.
Nutt, et al. (U.S. Pat. No. 6,631,284) presented a method to combine PET and X-Ray CT tomography for acquiring CT and PET images sequentially in a single device. Nutt, et al. summarized some available techniques to co-register and align functional and anatomical images and their usages.
Seeley, et al. (U.S. Pat. No. 6,856,827) presented a fluoroscopic tracking and visualization system. In the system of Seeley, et al., one image in the display is derived from the fluoroscope at the time of surgery. A fixture is affixed to an imaging side of the fluoroscope for providing patterns of an of array markers that are imaged in each fluoroscope image. A tracking assembly having multiple tracking elements is used to determine positions of the fixture and the patient. One of the tracking elements is secured against motion with respect to the fixture so that determining a position of the tracking element determines a position of all the markers in a single measurement.
Perskey (PCT Publication No. WO 02/096261) presents a method to accurately register three-dimensional CT or MRI images taken prior to an operation and integrate the images with real-time tracking positional data of the patient's body part and instruments operating thereon.
Gobbi, et al. presented “Correlation of pre-operative MRI and intra-operative 3-D ultrasound to measure brain tissue shift”, in K. K. Shung and M. F. Insana, editors, Medical Imaging 2000: Ultrasonic Imaging and Signal Processing, volume 3982 of Proceedings of SPIE, pages 77-84, 2000. In the system of Gobbi, et al., a set of infrared LEDs mounted on the ultrasound probe are used to track the location and orientation of the ultrasound probe so that the real time ultrasound images can be overlaid on the pre-operative MRI volume.
Piron, et al. (U.S. Patent Application Publication No. 2005/0080333) presented a hybrid imaging method to monitor medical device delivery and a patient support for use in the method. Particularly, MR imaging is used for the initial identification of tissue targets; and ultrasound imaging is then used to verify and monitor accurate needle positioning. The MR images and ultrasound images are co-registered based on measurements of fiducial markers obtained during the MR imaging procedure.
Keidar (U.S. Pat. No. 6,650,927) presented a method to render diagnostic imaging data on a three-dimensional map. The system of Keidar captures a three-dimensional (3-D) image of the structure including diagnostic information. A 3-D geometrical map of the structure is generated using a probe inserted into the structure. The image is registered with the map, such that each of a plurality of image points in the image is identified with a corresponding map point in the map. The map is displayed such that the diagnostic information associated with each of the image points is displayed at the corresponding map point. Typically, the system includes an ECG monitor to receive signals from one or more body surface electrodes, so as to provide an ECG synchronization signal.
Electrocardiogram (ECG, sometimes abbreviated as EKG) may be used for synchronization in collecting and/or combining data collected at the same or similar times relative to the cardiac cycle, usually based on the “QRS” complex or “R” wave of the ECG waveform. ECG looping of cardiac location specific data includes displaying collected ECG synchronized data/images sequentially through the ECG period, repeatedly in a continuous loop, such as image data and device location and/or orientation data (e.g., device portion position on or in contact with the heart).
ECG synchronization may include the detection and elimination of data from irregular or unusual ECG intervals or waveforms. For instance, modern MRI (Magnetic Resonance Imaging), Ultrasonic and CT (Computed Tomography) 3-D cardiac imaging systems incorporate these processes.
Cardiac catheter 3-D location systems, like the NOGA and CARTO systems, may incorporate these processes. Without ECG synchronization, the motion of the heart can cause very indistinct/low resolution cardiac images and varying device location information that can't be easily interpreted when images or location data or other data collected from different times in the cardiac cycle are combined. The NOGA and CARTO systems can display location data (and processed location data) recorded with ECG synchronization in synchronization with the patient's real-time ECG (synchronized ECG looping).
Some Electrophysiology (EP) navigation/ablation systems contain within them idealized or sample 3-D ECG synchronized images of the heart, which are displayed using synchronized ECG looping. At the same time, a multi-electrode device connected to the system is positioned in the patient's left ventricle (or other cardiac chamber) to record ECG waveforms, usually at 64 positions of known relative spacing. The ECG waveform data from the electrodes is processed to determine (compute) the de-polarization/re-polarization cycle of the adjacent tissues of the heart (the tissue electrical activity that produces the ECG and muscle contraction) and maps this data onto the synchronized ECG loop image data of the idealized or sample heart image, usually by color or pattern coding.
This provides a visual representation of the paths and patterns of the heart's electrical activation for diagnostic purposes (e.g., to identify abnormal cardiac tissue virtual locations that are self-activating or continuously activating each other in a loop and thus, disrupting the normal contraction pattern and/or contraction rate of the heart). This modified image is then recorded and displayed using synchronized ECG looping.
The multi-electrode device is removed from the chamber. When the ablation catheter connected to the system is inserted into the chamber, its tip and other electrode(s) sense ECG waveforms. The system computes at what location within the modified, idealized or sample heart image such a waveform would be produced based on the determined and recorded tissue activation pattern (de-polarization/re-polarization cycle) in the idealized or sample heart image and displays that position (usually as a colored ball or spot) within the idealized or sample heart image. Thus, the ablation catheter operator can guide the tip of the catheter to the damaged/malfunctioning tissue to destroy it and eliminate the aberrant electrical activation pattern.
Vesely, et al. (U.S. Pat. No. 5,797,849) presented a method for carrying out a medical procedure using a 3-D tracking and imaging system. In the system of Vesely, et al., the location of a surgical instrument, such as a catheter, is tracked and displayed relative to its immediate surroundings to improve a physician's ability to precisely position the surgical instrument. An imaging modality system is used to acquires 2-D, 3-D or 4-D image data sets from an imaging source, such as fluoroscopy, an MRI (magnetic resonance imaging), CT (computerized tomography of X-ray images) or 2-D or 3-D ultrasound device, to provide a “template” through or against which the shape, position and movement of instrument 1670 being tracked can be displayed. The template typically takes the form of an image of the environment surrounding the instrument (e.g., a bodily structure). If multiple (3-D) volumes are acquired at different time intervals, a 4-D image is obtained (e.g., 3-D image changing over time). Other methods and systems are also described in U.S. Pat. Nos. 5,343,865; 4,697,595; 4,596,145; 4,249,539; 4,694,434; 5,546,807; 6,241,675; 6,276,211; and 6,545,678.
Based on the 3-D coordinates of the individual transducers mounted to the instrument body, a 3-D image that would represent the position, size and shape of the instrument is constructed. The 3-D image of the instrument is placed in the correct spatial relationship with the underlying images showing the environment surrounding the instrument. For moving image sets, such as 2-D video loops, or 3-D ultrasound loops of the heart, the motion of the image data sets need to be output at a rate that continually matches that of the patient heart beat. To synchronize “video loops” with a patient's heart beat, a raw ECG signal is input into the processing computer.
One difficulty with ultrasound imaging has been visualization anomalies, including artifacts and overly bright images, in the ultrasonic images of catheters. Such artifacts can provide a misleading and inaccurate impression of the shape and/or location of the catheter within the patient. Additionally, catheter elements can appear so bright and large on the ultrasonic image (called “blooming”) due to their highly reflective nature relative to the anatomy, especially at the gain settings typically used to image the anatomy, that the image of the adjacent anatomy is obscured by the catheter image. For example, metallic portions of catheters can produce strong/high amplitude echoes (bright images), with a pyramid artifact (i.e., a pyramid shape of reverberation (“ringing”) images trailing off in the viewing direction). Similarly, most thermoplastic catheter shafts produce strong/high amplitude direct echoes (bright images). If the gain settings of the ultrasonic imaging system are reduced to improve the image of the catheter (reduce its image and artifact brightness), the image of the anatomy fades significantly to the point of being less visible or not visible at all. Therefore, it would be a significant advance to provide a catheter with improved imaging characteristics by two-dimensional and three-dimensional ultrasonic imaging systems for enhancing the diagnosis and guidance of treatments in the body.